The thermal barrier coatings (TBCs) are prepared using spraying technique of 8YSZ particles. In this process, H2 is often added to the plasma torch discharge system. In order to study the effect of H2 content on plasma discharge, this study emplyed particle velocity capture diagnostics, optical emission spectroscopy, and finite element simulation to validate the relationship between H2 content and coating quality. The results indicate that adding H2 increases the temperature and velocity of plasma, which in turn improves the efficiency and in-flight velocity of molten 8YSZ particles. However, when the H2 /(Ar+H2) is increased to 50%, the instability of arc root disturbs the arc plasma discharge, posing a challenge to maintaining the physical state of the in-flight particles. With an increase in H2 flow rate, the coating quality shows a trend of first increasing and then decreasing, with the optimal flow rate ratio being H2/(Ar+H2)=37.5%. The findings of this work can serve as a theoretical guidance and reference for the preparation of TBCs via plasma.